This dissertation presents a measuremeunt of the CKM matrix element |Vub| made with a sample of 64 million BB events collected with the BABAR detector. Using Heavy Quark theory, we combine the observed yield of leptons from semileptonic B decay in the electron energy interval 2.1–2.6 GeV with a recent CLEO measurement of the B → Xsγ photon spectrum to find |Vub| =(4.25±0.35±0.45±0.20)×10−3, where the first uncertainty is experimental and the last two are from theory.